[Illustration:  Fig. 1]

[Illustration:  Fig. 2]

The simplest arrangement for carrying out this method is shown in Fig. 1, which illustrates the arrangements at one end of a line.  M is the Morse key for sending messages, and is shown as in its position of rest for receiving.  The currents arriving from the line pass first through a “graduating” electromagnet, E2, of about 500 ohms resistance, then through the key, thence through the electromagnet, R, of the receiving Morse instrument, and so to the earth.  A condenser, C, of 2 microfarads capacity is also introduced between the key and earth.  There is a second “graduating” electromagnet, E1, of 500 ohms resistance introduced between the sending battery, B, and the key.  When the key, M, is depressed in order to send a signal, the current from the battery must charge the condenser, C, and must magnetize the cores of the two electromagnets, E1 and E2, and is thereby retarded in rising to its full strength.  Consequently no sound is heard in a telephone, T, inserted in the line-circuit.  Neither the currents which start from one end nor those which start from the other will affect the telephones inserted in the line.  And, if these currents do not affect telephones in the actual line, it is clear that they will not affect telephones in neighboring lines.  Also the telephones so inserted in the main line might be used for speaking to one another, though the arrangement of the telephones in the same actual line would be inconvenient.  Accordingly M. Van Rysselberghe has devised a further modification in which a separate branch taken from the telegraph line is made available for the telephone service.  To understand this matter, one other fact must be explained.  Telephonic conversation can be carried on, even though the actual metallic communication be severed by the insertion of a condenser.  Indeed, in quite the early days of the Bell telephone, an operator in the States used a condenser in the telegraph line to enable him to talk through the wire.  If a telephonic set at T1 (Fig. 2) communicate through the line to a distant station, T2, through a condenser, C, of a capacity of half a microfarad, conversation is still perfectly audible, provided the telephonic system is one that acts by induction currents.  And since in this case the interposition of the condenser prevents any continuous flow of current through the line, no perceptible weakening will be felt if a shunt S, of as high a resistance as 500 ohms and of great electromagnetic rigidity, that is to say, having a high coefficient of self-induction, be placed across the circuit from line to earth.  In this, as well as in the other figures, the telephones indicated are of the Bell pattern, and if set up as shown in Fig. 2, without any battery, would be used both as transmitter and receiver on Bell’s original plan.  But as a matter of fact any ordinary telephone might be used.  In practice the Bell telephone is not advantageous